Danielle a hurricane; TD 7 forming off coast of Africa

Hurricane Danielle has stopped intensifying and is now looking a bit ragged this morning, but remains a respectable Category 1 hurricane with 80 mph winds. The intensity of Danielle's heavy thunderstorms has waned in the past few hours, and the organization of the storm is less impressive. This is probably due do strong upper-level winds out of the west that are creating a moderate 10 - 20 knots of wind shear, and injecting some of the dry air from the Saharan Air Layer (SAL) that surrounds Danielle. Danielle is over warm 28°C water, but is far from any land areas.

Figure 1. Morning satellite image of Tropical Storm Danielle (left side of image) and the forming Tropical Depression Seven (right side of image.)

Forecast for DanielleA powerful trough of low pressure over the mid-Atlantic Ocean will begin to pull Danielle more to the northwest by Wednesday, keeping Danielle well to the east of Bermuda. Most of the models predict that this trough will be strong enough to fully recurve Danielle out to sea. It is possible that Danielle could eventually threaten Newfoundland, Canada, but it currently does not appear that any other land areas will be at risk from this storm. History suggests that a storm in Danielle's current location has only a 20% chance of making landfall on the U.S. East Coast. If Danielle passes east of Bermuda, as forecast, these percentages drop to less than 5%. As far as intensity goes, it is looking unlikely that Danielle will attain major hurricane status (115+ mph winds.) There is enough dry air and wind shear affecting the storm today that it will take several days for the storm to recover its strength, making it less likely the storm can hit Category 3.

The formation of Danielle is remarkable in this it was successfully forecast by the GFS model nearly two weeks in advance. The ECMWF and NOGAPS models also did a good job of predicting Danielle's formation a week in advance. The models are getting better and better each year at forecasting genesis of tropical cyclones, though a successful 1-week forecast of genesis is still a rarity. For example, none of the models foresaw the development of 96L until just 3 - 4 days ago.

Figure 2. Plot showing historically the percent chance of a tropical cyclone in a given location impacting the U.S. East Coast. For storms in Danielle's current position (orange hurricane symbol), about 20% of them go on to hit the U.S. East Coast. For storms in 96L's current location (red circle with a "?" in it), the odds are also 20%. Image credit: Bob Hart, Florida State University.

96L (soon to be Tropical Depression Seven)Satellite images suggests that a tropical wave (96L) that emerged off the coast of Africa yesterday morning has developed a closed circulation, low-level spiral bands, and an increasing amount of heavy thunderstorms. While this morning's ASCAT pass does not show a clear closed circulation, satellite estimates of 96L's strength support calling this a 30 mph tropical depression. It is likely that this storm will be designated Tropical Depression Seven later today. 96L is already bringing heavy rain and strong, gusty winds to the southern Cape Verde Islands. Winds were sustained at 26 mph at Mindelo in the northwest Cape Verde Islands this morning, and 24 mph at Praia, the station closest to the center of 96L. Both stations were reporting widespread dust, due to strong winds blowing Saharan dust from the coast of Africa. However, water vapor satellite images show that only a modest amount of dry air is accompanying this dust, and dry air is currently not a major detriment to 96L. Wind shear is about 10 - 20 knots, and sea surface temperatures are warm, 28°C.

Forecast for 96L/Tropical Depression SevenWind shear is predicted to remain low, 5 - 10 knots, for the next four days. SSTs will cool a bit to 27°C by Thursday, but this is still above the 26.5°C threshold for hurricane development. Dry air will probably be the main inhibiting factor for 96L. Most of the intensity forecast models bring 96L to hurricane strength by four days from now, and this is a reasonable forecast. 96L should become Tropical Storm Earl later today or on Wednesday, and will probably bring sustained winds of 40 mph to the southernmost Cape Verdes Islands tonight and Wednesday.

The long range fate of 96L remains unclear. The storm is being steering by the same ridge of high pressure steering Danielle, and will initially follow a track similar to Danielle. 96L may encounter the cold waters stirred up by Danielle at times this week, inhibiting development. As 96L approaches the central Atlantic five days from now, the storm will encounter the same mid-Atlantic trough that will be steering Danielle, and 96L should turn more to the northwest. It is unclear at this point whether this trough will be strong enough to fully recurve 96L out to sea, east of Bermuda. This will, in part, depend upon how strong Danielle gets. A stronger Danielle is likely to create more of a break in the ridge of high pressure steering 96L, encouraging the storm to turn north and recurve out to sea. A weaker Danielle will make 96L more likely to miss recurvature, and follow a track to the west or west-northwest towards the U.S. East Coast early next week. History suggests that a storm in 96L's current location has only a 20% chance of making landfall on the U.S. East Coast.

When will the Caribbean and Gulf of Mexico get active?The large scale atmospheric circulation over the Caribbean and Gulf of Mexico currently features relatively dry, stable, sinking air. This is due, in part, to the Madden-Julian oscillation (MJO). The Madden-Julian oscillation is a pattern of enhanced rainfall that travels along the Equator from west to east. The pattern has a wet phase with large-scale rising air and enhanced thunderstorm activity, followed by a dry phase with large-scale sinking air and suppressed thunderstorm activity. Each cycle lasts approximately 30 - 60 days. When the Madden-Julian oscillation is in its wet phase over a hurricane-prone region, the chances for tropical storm activity are greatly increased. The latest MJO forecast from the GFS model calls for the wet phase of the MJO to move into the Caribbean during the first week of September. However, keep in mind that forecasts of MJO activity 1 - 2 weeks in advance are not very skillful. The GFS model forecast of MJO activity made two weeks ago did fairly well for the first week, but poorly for the second week of the forecast.

Tropical Storm Frank spares MexicoOver in the Eastern Pacific, Tropical Storm Frank has moved away the coast far enough from the Mexican coast to no longer pose a heavy rainfall threat, and all tropical storm warnings have been dropped.

"Hurricane Haven" airing again this afternoonTune into another airing of my live Internet radio show, "Hurricane Haven", at 4pm EDT today. Listeners will be able to call in and ask questions. The call in number is 415-983-2634, or you can post a question in the comments area on my blog during the show. You can also email the questions to me today before the show: jmasters@wunderground.com. Be sure to include "Hurricane Haven question" in the subject line. I'll focus on Danielle, Earl, and Frank, and discuss the possibilities of a hyperactive Atlantic hurricane period coming during the first week of September.

Quoting aislinnpaps:I am trying to remember the last Major Hurricane to threaten the Metro NYC area. Gloria in the 1980's comes to mind.

The problem with a hurricane, especially a major one, hitting New York is they don't prepare. I was up visiting in the 80's on my way back from Germany. I was the only one concerned, the only one to even do a little preparing. Having lived in Texas and Louisiana, I knew what a hurricane can do. Up there they just teased me for being concerned.

They really can't evacuate, can they? Could be disastrous. I saw one of those, "what if show" once. The sub city was underwater from a direct hit.

I am trying to remember the last Major Hurricane to threaten the Metro NYC area. Gloria in the 1980's comes to mind.

The problem with a hurricane, especially a major one, hitting New York is they don't prepare. I was up visiting in the 80's on my way back from Germany. I was the only one concerned, the only one to even do a little preparing. Having lived in Texas and Louisiana, I knew what a hurricane can do. Up there they just teased me for being concerned.

What kind of impact or "pull" does a full moon have on hurricanes or storms? Got me curious. TIA

Quoting txjac:

What kind of impact or "pull" does a full moon have on hurricanes or storms? Got me curious. TIA

I think maybe at landfall, the tides could be higher and then it would be a greater effect on the coast it hits, if any. Also, you can see the storm on visible satellite , longer, I've noticed, due to the extra light.

Now perhaps the only thing I'm truly confident in regarding hurricane forcasts is the notion that patience is truly a virtue in these matters. The long range forcasts change and are altered every few hours.

That said, since it's the topic du jour, is forward moving speed a big factor in storms hitting New England and beyond? I have been reading the hurricane histories on the NOAA site and it seems like all the ones striking the NE were described as "rapidly accelerating". If I'm right, and it is a big factor, can we predict whether the current system will pick up speed??

Quoting lou60carol:i remember in 54and 55carol and diane hit north carolina and up to new england the storms went south of burmuda and toward the ncand up to n e thanks

we lost the roof off our '52 buick convertible going over the gw bridge into ny during hazel. i was 3, one of my first memories. the rain stopped after we got into the city. only hurricane i've ever been in.

Also, despite how inaccurate the GFS is at that long range, it still doesn't develop anything over the entire Gulf of Mexico or Caribbean (except that little blip over Puerto Rico at the end). It just shows a continuous train of waves coming off of Africa. I guess I can't complain, 6 storms in 2 weeks none of them strike CONUS, except for maybe Danielle hitting the North East.

Its more the idea that the models continue to trend west and have for about a day now.

Also it does work the other way; why is it when a run takes it out to sea you think it is believable and yet when it takes it further west you think its crazy and should not be trusted?

I don't think anything one day from the next, just making an observation about many bloggers here at wu. You must admit, many find it more exciting when a storm model takes it close to land and tend to believe it (or want to), however, if it's a re curve out to sea, many dispute the model more often. Check past blog entries for yourself. Like I said, just an observation on my part. No big deal.

Quoting ShenValleyFlyFish:Yea, sort of like the guy who brought a lawnmower into the machine shop where I worked. He told the guy at the desk that "the integrity of one of the joints was severely compromised." When we got it in the shop we discovered one side of the push handle had almost broken off.

Too funny KanKunKid. I couldnt believe that Ike made it to Ohio. I live in Texas and my mom was all worried about it here. And then it winds up in Ohio (where she lives) and she got roof damage and had to replace it

Quoting MiamiHurricanes09:I would not be surprised at all if the GFS verifies with the 6 named storms in a 2 week span. I mean, it's that time of year, we're in a bad pattern, it's about time that things pop, and the GFS is definitely showing us. We might be up to Fiona by Sunday.

I still think Danielle hitting the East Coast is a bit far fetched, but storms coming in from behind it have a better chance. Different ridging conditions, and a "guiding" high pressure could cause closer calls.